The present invention relates to the building of a pneumatic tire, and concerns a method and apparatus for reinforcing a butt splice along the edges of two reinforced elastomeric sheets to form an elastomeric member such as that used in the tire industry for the manufacture of a tire carcass.
As conventionally known in the tire manufacturing art, it is a common practice to join or splice the edges of two reinforced elastomeric sheets to form an elastomeric member used for the manufacture of a tire carcass.
Each of the reinforced elastomeric sheets contains a plurality of parallel reinforcing cords encapsulated within an unvulcanized synthetic or natural rubber. The reinforcing cords are substantially equal in diameter and evenly spaced between one another within the sheet. For the manufacture of a tire carcass, particularly when producing radial ply tires, the elastomeric sheets are typically cut into rectangles, which are then assembled to each other by means of a splice along adjoining edges of two adjacent sheets, the splice being parallel to the reinforcing cords.
Two commonly used splices join the edges of adjacent sheets are the butt splice and the overlap splice. The butt splice is formed by pressing one edge of one sheet against an adjacent edge of a second sheet and securing them together by mechanical or physical means, i.e. pressing them together to ensure that they are securely bonded. The overlap splice is made by covering an edge of one sheet by an adjacent edge of a second sheet, and applying pressure to the splice area which includes the overlapped region to ensure a secure bond. The double thickness of the overlap splice in the splice area has several drawbacks. These include the uneven elongation of the elastomeric member due to the difference in elongation of the narrow region of double thickness as compared with the elongation of the elastomeric member in the region of single thickness. This difference in elongation can lead to the creation of a non-uniformity in the resultant tire.
The butt splice overcomes the drawbacks of the overlap splice, i.e. has a single thickness. However, the smaller contact surface between the adjacent edges of the two sheets being assembled together inherently creates a weaker bond between the two sheets than the bond formed with the overlap splice. Also, a successful butt splice is more difficult to consistently achieve in a manufacturing environment as it depends on the proper preparation of the edges of the elastomeric sheet to ensure that the spacing between the cords at the two adjoined edges of the butt splice is no greater and no less than the spacing between the remaining cords in the sheets. Either condition, i.e. the spacing between cords along the edges of the two sheets being assembled being either greater or less than the spacing of the other cords in the two sheets, can result in non-uniform strength across the resulting elastomeric member, uneven stretching of the elastomeric member during its expansion while forming the tire carcass, and a greater likelihood of splice failure in the resultant tire.
Another approach toward reducing or eliminating the problems associated with effectively splicing together two reinforced elastomeric sheets is to bridge the butt splice with a reinforcing strip extending the length of the splice. This approach provides a partial solution to the problem because it was always accomplished by manually applying the reinforcing strip. Until now, no one has been able to effectively apply the reinforcing strip in a manufacturing environment. Moreover, the manual application of the reinforcing strip was not a completely satisfactory solution because of the inherent variations in the thickness and length of the reinforcing strip and the added manufacturing time and costs associated with the manual application of the reinforcing strip.
A further attempt to reduce the adverse effects of using a reinforcing strip to bridge the butt splice of reinforced elastomeric articles is described in U.S. Pat. No. 5,062,462 (""462), issued Nov. 5, 1991 and having a common assignee with the present invention. This ""462 patent describes the use of a thin splicing strip made from a spun bonded material having stress/ strain/ expansion characteristics closely resembling those of the elastomer in the article. The splicing strip is manually applied across the area being spliced, contributing to increasing the labor costs associated with construction of a tire using a butt splice.
U.S. Pat. No. 4,328,066 (""066), issued May 4, 1982, describes a tape splicing apparatus in which two tapes are joined by splicing tape. The apparatus addresses a problem of entrapping air bubbles under the splicing tape. A drum body (59) holds a splicing tape segment (T3) by suction pressure applied through holes in the peripheral surface of the drum. The drum is lowered into a splicing position to press the sticky side of the tape segment against the abutting tape joint, and the tape segment is initially attached along only a single line. It is frequently observed that only the portion of the splicing tape segment which corresponds to the butt joint is stuck to the abutted tapes, with the remaining portion(s) left curled upwardly (see column 10, lines 29-34). A separate mechanism, in the form of a movable depressing roller (94), then presses the splicing tape segment, which was initially attached along only the single line, in forward then rearward directions from the center of the joint so that no air can be entrapped under the splicing tape. (see Abstract)
It is an object of the present invention to provide a method and apparatus for applying a splice strip along a butt splice of two elastomeric sheets as defined in one or more of the appended claims and, as such, having the capability of accomplishing one or more of the following subsidiary objects.
Another object of the present invention is to provide a method and apparatus for improving the repeatability and reliability of the butt splice of reinforced elastomeric sheets.
Yet another object of the present invention is to provide a method and apparatus for increasing the rate for butt splicing reinforced elastomeric sheets while concomitantly reducing the labor costs and the overall expense of effectively splicing the two sheets together.
The present invention relates to a method of butt splicing the edges of two elastomeric sheets. The elastomeric sheet can be, if desired, reinforced with parallel cords of a non-metallic material such as polyester, cotton, rayon, nylon or aramid or of a metallic material such as for example filaments of steel which have been plated with brass. In the reinforced elastomeric sheets, the cords run parallel to one another and to the edges of the sheets being assembled together, and are evenly spaced from one to another in the sheets. The method includes the steps of securing adjacent edges of two elastomeric sheets together with the butt splicing technique. Then a thin splice strip of an uncured elastomer such as gum rubber, preferably reinforced with cords or a non-woven fabric, is applied across the butt splice securing the elastomeric sheets together. This is accomplished by first locating the splice strip onto an applicator head and holding it in place by a vacuum. The applicator head is then moved to press the splice strip against the butt splice. After the splice strip is securely in place, the vacuum is removed to release the splice strip from the applicator head and the applicator head returns to pick up another splice strip.
The applicator head is preferably rotated from a first load position where the splice strip is loaded on the head to a second position in close proximity to the butt splice. From there, the applicator head is moved to a third position where the splice strip can be pressed into contact with the butt splice. The splice strip is preferably the same length as the butt splice.
A second splice strip is loaded onto a second applicator head in the load position while the first applicator head is in the second position either before or after applying the splice strip onto the butt splice with the first applicator head. The second splice strip is held to the second head by vacuum in the same manner as the first splice strip is to the first head. The second applicator head is rotated into the second position as the first applicator head is rotated away from the second position in proximity to the butt splice and back to the load position. The second splice strip is then pressed into contact with a second butt splice and the vacuum is released to free the second splice strip from the second applicator head. The first and second applicator heads can be moved between the first load position and the second position by oscillating back and forth through an arc of 180xc2x0 or by rotating in the same direction, and stopping each 180xc2x0 to load one splice strip onto one applicator head while the other applicator head is at the second position above the third location while the other splice strip is applied onto the second butt splice.
The invention further includes a method of reinforcing a butt splice along the edges of two adjacently disposed elastomeric sheets, comprising the following steps. A splice strip is loaded on an applicator head at a first load position. The applicator head is moved to press the splice strip into contact with the butt splice. The applicator head is moved from the first load position to a second position in proximity to the butt splice. Then the applicator head is moved to a third position where the splice strip is first pressed into contact with the butt splice and subsequently the vacuum is released. Next, the splice strip is released from the applicator head by releasing the vacuum pressure used to hold the splice strip on the applicator head. The method can further include the additional steps of placing a second splice strip on a second applicator head in the load position; moving the first applicator head away from the butt splice after releasing the first splice strip; moving the second applicator head to the second position and then to the third position to press the second splice strip into contact with a second butt splice; and releasing the second splice strip from the second applicator head. The first applicator head and the second applicator head are oscillated or rotated through an arc of 180xc2x0 between the first load position and the second position.
The invention also includes a splice strip applicating device for applying a splice strip over a butt splice. The device comprises a first applicator head, structure for applying and temporarily holding a splice strip in a first load position on the first applicator head, structure for moving the first applicator head to a second position into pressure contact with the butt splice, and structure for releasing the splice strip from the first applicator head. The device preferably includes a second applicator head disposed so that the first and second applicator heads are mounted in diametrically opposed relationship to one another with respect to the axis a shaft adapted for rotating or oscillating movement about the axis of the shaft. This arrangement of the splice strip applicating device permits the first applicator head to be in the splice strip load position while the second applicator head is in the second position 180xc2x0 around the axis and in close proximity to the butt splice. The device includes a dispenser for feeding a length of the splice strip onto either of the applicator heads in the load position. It also includes a gripper to clamp on to a length of splice strip and to load the splice strip on one applicator head, and a cutter to cut the splice strip to a predetermined length while being held on an applicator head.